It is very crucial to fine out how search engine find duplicate content from your site. It is easy to make website very clear and effective if it have 5 to 50 pages but this discussion come into action for large database driven websites. If your website is product base then it should have thousands of pages. Webmaster and site owner need to focus on website page duplication. In most cases duplication start from the URL parameters like session IDs or Tracking IDs.
How tracking IDs and Session IDs cause duplication?Tracking IDs and Session IDs are used to help and store user information and this is the main source of duplication. All user information go through session ID and this will cause duplicate content and create similar pages for different users.
How it will affect search engine ranking?
Search engine try to crawl as many pages identical pages but with session IDs or tracking IDs same page generate number of times and this will become main resource of duplicate content.
Also with session ID URL become user-unfriendly and it will decrease chances of selecting the listing.
How to protect your website from duplicate URL problem?
Here is the clue about protecting your website from duplication. You can ask your developer to re-write URL using .htaccess or any other good URL rewriting tools. Try to make URLs possible sort in length. If your website have number of same page with different session IDs then you can do permanent redirect (301) that will help you much.
How do I know if Google find duplicate pages from my website?Day by day Google and other major searching try to give accurate results and also try to help webmaster for optimizing website. Google is ahead in the race, they have clearly mentioned
1. When we detect duplicate content, such as through variations caused by URL parameters, we group the duplicate URLs into one cluster.
2. We select what we think is the "best" URL to represent the cluster in search results.
3. We then consolidate properties of the URLs in the cluster, such as link popularity, to the representative URL.
SEO & Web Promotion Expert.